A modified Koistinen and Marburger (KM) kinetics model including the average prior austenite grain size (PAGS) variable was proposed. The enhancement was achieved by introducing the relationship between PAGS and temperature point \({T}_{0}\) , at which the transient change rate is the maximum in the evolution of the phase transformation rate parameter \(\alpha \) , thereby improving the accuracy of martensitic transformation kinetics prediction. Diverse austenitization temperatures were applied to investigate the effect of PAGS on the martensite transformation of cold-rolled quenching and partitioning (Q&P) steel during the decomposition of austenite. An increase in PAGS from 3.8 to 19.3 μm was observed with elevated austenitization temperatures, accompanied by a sigmoidal rise in martensite start temperature \({M}_{\text{s}}\) . And the relationship between PAGS and \({M}_{\text{s}}\) was quantitatively described through an exponential function. At the same time, the martensite fraction at the same quenching temperature gradually increased with the increase in PAGS, leading to the development of PAGS-incorporated modified KM model. The model accurately predicts PAGS-dependent martensite transformation kinetics in Q&P steels across various austenitization temperatures, enabling multi-process kinetic curve predictions and overcoming the limitation of process-specific and single-curve prediction in existing models, with significantly broadened applicability.
